Within the above mentioned technical area many different solutions exist to improve a sawblade by varying and changing the teeth of the sawblade in different ways to increase the safety and efficiency when using a saw.
The most common sawblades on the market are group-toothed blades (that is blades with irregular distance between the tooth-tips) the number of teeth can be 3, 4 or 5 teeth per inch.
When manufacturing group-toothed sawblades a punching tool consisting of punch and die with the same profile as the blade being produced is normally used. With this tool one can only produce sawblades with one type of toothing.
One purpose in making a sawblade with teeth in group is to neutralize the resonance that easily occurs in a sawblade that has been fastened in an arc. The blade may then act like a string on a guitar, that has a given tone.
In a sawblade without teeth in group vibrations easely occur, as the tooth-tips of the sawblade can strike against the wood-fibers. This can be compared to the tooth-points acting like a number of small axes chopping off the wood-fibers at an even frequency. The chance is great that this frequency is equivalent with the that of blade itself, so that resonance occurs, causing vibrations in the sawblade.
This can be shown by the following example. If you assume that a 30" (762 mm) long blade with 150 teeth has a tension that gives a normal A (440 Hz) in frequency and the saw is moved at a speed that gives one sawstroke in 0.34 second, which is a fairly normal speed, the points will strike against the treefibers with a frequency that corresponds with the sawblades own frequency. This leads to resonance and accompanying strong vibrations.
Corresponding risks for resonance naturally exist at other sawing speeds that are equivalent to different under and overtones, like an octave or a quint etc. The result of this is that the sawblade tends to brake in the sawtrack which leads to more heavy sawing.
These problems has been solved through the arrangement of irregular distance between the points.
This causes several tones to occur (dissonance). These vibrations neutralize each other making that the saw goes "quiet", that is, free of vibrations and accordingly running easier in the track.
Saws for fast cutting have relatively big teeth. With this type of toothing it is difficult to begin a sawstroke, that is, from a level where the speed of the sawblade is 0 and hereby being able to make a sawstroke avoiding that the sawblade jumps risking an injury both in the hand that is holding the work-piece and the work-piece itself. Injuries of this kind are one of the most common on constructing-sites, they cause much inconvenience and a lot of unnecessary suffering.
One solution to the problem with jumping bowsaws is the so called push-off sawblade, that is, a sawblade with fine teeth in the front part of the blade, with the purpose to make the start of the stroke easier, followed by bigger teeth for higher performance.
When manufacturing a sawblade with finer, closer toothing in the front of the blade, within the intention that one at the start of a cutting (that is, from the level where the speed of the sawblade is 0) shall be able to make a sawstroke without the saw jumping, one has up to now had to cut the blade in several different tools.
Some examples of different constructions and production methods for sawblades are shown in EP-A1-205 245, DE-C-565 136, FR-A-1 586 519 and GB-A-2 177 344
Short presentation of the invention idea. PA1 Short description of attached drawings.
The purpose of the invention in question is to provide a sawblade for instance for bowsaws (arcsaws), that unites the advantages of both the types of blades mentioned above and at the same time is easy and cheap to manufacture.
In accordance with the inventionidea one receives a sawblade with at least one push-off part and at least one part with teeth in group, wherein the part of the blade with teeth in group includes a number of groups of preferably V-shaped notches in the blade, wherein each pair of notches defines a sawtooth, and wherein each group is comprised of an even number of notches, and that an imaginary line A that is drawn between each alternate bottom of a selected group, e.g. notch one, three, five, etc. is a straight line which establish a small angle, alfa, to the longitudinal direction of the sawblade whereby the bottoms and the tips are uniformly distributed along the line.
According to the inventionidea a group-toothed sawblade is produced by means of a tool comprised of a punch and a die, wherein the punch cutting out the sawteeth is constructed fully symmetrically with essentially V-shaped points, wherein a sawblade-blank conveniently in the form of a steel-bandis fed through said tool, and the blank is punched in at least two stages with one and the same tool wherein the blank for the purpose of forming one group in a group-toothed part in a first stage from a starting position is tilted a small angle, alfa, relative to the punchingtool and the blank is punched against the die, whereafter the blank is advanced through the tool a distance which corresponds to half the width of a tooth, calculated on a punchingtool tooth, and the blank in a second step is tilted back relative to the tool in an opposite direction to at least the starting position and is punched, whereafter the method is repeated until the desired number of groups have been formed.
By combining the quiet stroke of the group-toothed sawblade with the safety of the push-off toothed blade, one receives a sawblade that is easy to saw with, since the resonance in the blade almost has been eliminated and the chance that the saw jumps and causes the user injuries in the start is very small.